Self-cleaning aperture tube for coulter study apparatus and electrolyte supply system therefor

ABSTRACT

A two chamber aperture tube for obtaining signals from particles suspended in a fluid which passes through a scanning aperture. The suspension enters an aperture in an inlet chamber and passes thereafter to an outlet chamber in fluid connection with the inlet chamber. The inlet chamber of the tube is connected to a source of clean electrolyte; the outlet chamber is connected to a waste collecting container. A vacuum is applied to the collecting container to cause clean electrolyte to be drawn through the inlet chamber and wash behind the aperture simultaneously with passage of the suspension through the aperture. A restriction in the path of flow of the clean electrolyte causes the flow velocity thereof to increase behind the aperture and ensure that proper signals from all particles in the suspension are obtained.

United States Patent Hogg et 2].

[Ill 3,902,115

Aug. 26, 1975 SELF-CLEANING APERTURE TUBE FOR COULTER STUDY APPARATUS AND ELECTROLYTE SUPPLY SYSTEM THEREFOR Primary ExuminerAlfred E, Smith Assistant E.\aminer-Rolf Hille Attorney Agenh or Firm-Silverman & Cass Ltd.

[ 57 l ABSTRACT A two chamber aperture tube for obtaining signals from particles suspended in a fluid which passes through a scanning aperture. The suspension enters an aperture in an inlet chamber and passes thereafter to an outlet chamber in fluid connection with the inlet chamber. The inlet chamber of the tube is connected to a source of clean electrolyte; the outlet chamber is connected to a waste collecting container. A vacuum is applied to the collecting container to cause clean electrolyte to be drawn through the inlet chamber and wash behind the aperture simultaneously with passage of the suspension through the aperture. A restriction in the path of flow of the clean electrolyte causes the flow velocity thereof to increase behind the aperture and ensure that proper signals from all particles in the suspension are obtained 32 Claims. I} Drawing Figures Z 5; 59 /7 nav mmm m 26 m5 SHZU 1 [IF 4 PATENTED Auszsma 111T 2 OF 4 PAIENTEU auszsms SHEET 3 BF 4 QNY SELF-CLEANING APERTURE TUBE FOR COULTER STUDY APPARATUS AND ELECTROLYTE SUPPLY SYSTEM THEREFOR CROSS-REFERENCE TO RELATED PATENTS The structure to which this invention applies is of the type described and disclosed in U.S. Pat. No. 3,299,354 (herein called the Related Patent") issued Jan. 17, 1967 for "Aperture Tube Structure for Particle Study Apparatus to one of the applicants herein, and owned by the same assignee as the invention herein. The said Related Patent is incorporated herein as a part hereof by specific reference.

The herein invention also is related to and is an improvement upon the structure disclosed in U.S. Pat. No. 3,746,976 issued July 17, 1973 for Self-Cleaning Aperture Tube for Coulter Study Apparatus", the applicant therein being one of the inventors herein, and owned by the same assignee as this invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to the art of studying the physical properties of particles carried in suspension and more particularly is concerned with improved apparatus for obtaining signals from particles passing through a scanning aperture without extraneous interference from other particles.

2. Description of the Prior Art The structure disclosed in the Related Patent substantially decreases the possibility of undesirable spurious particle reading and count signals which sometimes occured in prior art devices. This was accomplished by replacing the so-called aperture tube of prior art structures with a pair of chambers having an interconnection for separating the electrical and mechanical effects produced by particles passing through the aperture. Particles passing through the aperture of the apparatus immediately were transported away from the proximity of the aperture so that there was little or no chance of spurious signals resulting from said particles.

One of the objects of the invention disclosed in the Related Patent was to provide an aperture tube which was self-cleaning in that the suspension in the immediate vicinity of the aperture was kept free of extraneous particles. As acknowledged in the patent, however, eddy currents of fluid in the aperture tube at the downstream end of the primary bore could occur, and these eddy currents swirled into the secondary bore immediately adjacent the primary bore. It was believed that the fluid would be stagnant liquid substantially devoid of particles, hence not introducing appreciable extraneous signals, but while this was largely true, the action was deemed not sufficient to satisfy the more critical demands of today's technology. A small percentage of particles was not caught by the orifice in the elongate neck of the second chamber and these sometimes produced extraneous signals by virture of the eddy currents at the bottom of the central chamber of the aper ture tube.

For purposes of resolving the aforesaid problems with regard to extraneous signals, the invention disclosed in U.S. Pat. No. 3,746,976 provides a selfcleaning aperture tube as disclosed in the Related Patent, with the addition of a pump device interposed between the first and second chambers to produce a closed system in which there are no inlets or outlets other than the primary bore in the first chamber. The pump operates to draw the particle suspension up through the second chamber and force the same back into the first chamber, completing a circuit around this path and creating a sheath flow at the orificev The flow created by the pump is such as to ensure that all parti cles introduced into the aperture tube are caught by the orifice of the second chamber so as to prevent the occurrence of extraneous signals.

The invention of U.S. Pat. No. 3,746,976 satisfactorily eliminates the extraneous signal problems inherent in the structure of the Related Patent. In so doing, however, the structure incorporates a pump and filter through which electrolyte is recirculated to achieve the cleaning flow. Further, the structure of U.S. Pat. No. 3,746,976 includes a relatively fragile and cumbersome aperture tube in which the chambers thereof are sepa rated along a substantial portion of the tube.

SUMMARY OF THE INVENTION The present invention provides an improved selfcleaning aperture tube for a Coulter study apparatus of the type disclosed in the Related Patent. (The mark Coutler" is the registered trademark, Registration No. 995,825 of Coulter Electronics, Inc. of Hialeah, Fla. The aperture tube of the herein invention eliminates the disadvantages of the tube disclosed in U.S. Pat. No. 3,746,976 in which one chamber has a branch or lateral diversion which passes out of a second chamber and returns again. Further, the present invention provides a system which supplies fresh clean electrolyte from a reservoir and eliminates the need for recirculating the electrolyte through a pump and filter as in the structure of U.S. Pat. No. 3,746,976.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view through a system constructed in accordance with the invention, including some diagrammatic representation of associated apparatus for the purpose of explaining the same;

FIG. 2 is a fragmentary enlarged sectional view through the aperture tube of the invention showing the details thereof;

FIG. 3 is a view similar to that of FIG. 2 illustrating a modified construction of the aperture tube;

FIG. 4 is a view similar to that of FIG. 2 illustrating a further modified construction of the aperture tube;

FIG. 5 is a fragmentary enlarged sectional view of another form of aperture tube for use with the structure of FIG. 1;

FIG. 6 is a fragmentary enlarged sectional view of a still further form of aperture tube for use with the structure of the invention;

FIG. 7 is a fragmentary enlarged sectional view of another alternate embodiment of the aperture tube for use with the structure of the invention;

FIG. 8 is a sectional view taken along the line 8-8 of FIG. 7 in the direction indicated generally;

FIG. 9 is a sectional view taken along the line 99 of FIG. 7 in the direction indicated generally;

FIG. I0 is a fragmentary enlarged sectional view of an additional alternate embodiment of the aperture tube for use with the structure of FIG. 1;

FIG. 11 is a sectional view taken along the line IIl1 of FIG. 10 in the direction indicated generally;

H0. 12 is a sectional view taken along the line 12-12 of FIG. in the direction indicated generally; and

FIG. 13 is a sectional view taken along the line 1313 of FIG. 10 in the direction indicated generally.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus with which the structure of the invention is intended for use is known as the Coulter electronic particle analyzing device. The Coulter device and its principle of operation is referred to with particularity in the Related Patent. Since the Related Patent is incorporated herein as a part hereof by specific referencc, the disclosure thereof will not be repeated except in instances where understanding of the invention herein will be enhanced.

Referring to FIG. 1, the structure of the invention is indicated by the reference number 10. A dual chamber aperture tube 12 including a first chamber 13 which is formed upon and completely surrounds a second chamber 18, is suspended within a vessel or beaker 38. A measuring aperture 14 is formed in the wall of the first chamber 13 near the lower end thereof; a cleaning orifree 16 is formed in the wall of the second chamber 18 in registry with the aperture 14. The vessel 38 retains a body of the sample solution 48 to be drawn through aperture 14 and orifice 16; electrodes 34 and 36 are positioned within the aperture tube 12 and vessel 38, respectively, and are connected to the detector of a Coulter study apparatus through leads 17 in the manner described in the Related Patent for purposes of performing an analysis of the sample solution.

Aperture tube 12 is associated with the structure 10 by mounting same on coupling block 54 which is separable along the juncture line 56, the two portions 57, 58 of block 54 being secured together by screws 59. The tube 12 terminates within the block 54 at its upper end 62. An O-ring 64 is positioned about tube 12 to provide an air and liquid-tight seal. The tube is secured by cast epoxy resin to the lower half 57 of block 54 to form an easily mounted integral assembly. The tube 12 thereby may be replaced readily with another of the same type in the event of breakage, or with an alternate form of tube as discussed hereinafter. A conduit 71 with valve 73 for flushing and purging the tube 12 is connected to the tube by fitting 70.

Chamber l8 terminates downstream in the upper portion 19 thereof at a fitting 21 which couples the terminal portion 19 to a conduit 20. A valve 22 is positioned in conduit and the conduit terminates at a waste drip chamber or waste container 24. A vacuum source (not shown) is connected to the waste container 24 by conduit 23. A waste conduit 42 with valve 43 is provided on the bottom of container 24.

Chamber 13 forms the upstream portion of structure 10. The upper port 25 of chamber 13 is connected by couplings and conduits designated generally 80 through the choke" or hydraulic resistance 27 to an electrolyte supply drip chamber 29 having access ports 31 and 35, normally closed by valves not shown, and a supply port 33. Clean electrolyte 28 is supplied to chamber 29 through supply reservoir 52 which empties into reservoir 26 and is drawn into the chamber through fluid connection 40 having a valve 30 interposed therein.

A shield represented by the dashed line 32 is provided electrically to insulate connecting members and supply drip chamber 29 when the electrode 34 serves as the signal electrode for the Coulter study apparatus. This will be the case when more than one aperture are immersed in the sample bath 48 of vessel 38. [f a single aperture tube 12 is used in the sample bath, the electrode 34 may be grounded and the electrode 36 may be the signal electrode in which case the shield 32 may be omitted. Since the electrolyte path 40 between valve 30 and the aperture tube 12 is broken by the drip chamber 29, it may be grounded and located at any convenient position regardless which electrode is used as the signal electrode.

The waste bottle/waste drip chamber 24 will serve one or the other function depending upon the application and desired mode of operation of the structure of the invention. If the bottle/chamber 24 has a volume greater than the combined sample and clean "wash electrolyte. and the waste is evacuated after each measurement through tube 42 by opening valve 43, the bottle/chamber 24 will serve merely as a drip chamber and the electrical connection will be broken between the electrolyte path through the tube 42 and the electrolyte path through the tube 20 and valve 22 by means of the droplet formation indicated at 41. If the valve 43 is not opened after each measurement cycle, the bott le/chamber 24 must have a much larger capacity and will serve as a waste bottle.

Operation of the structure 10 is as follows: a vacuum is applied from the vacuum source through conduit 23, the waste bottle/drip chamber 24, valve 22 and tubing 20 to the inside chamber 18. Assuming that the aper ture 14 is plugged, suction is applied to the orifice 16, which in turn sucks liquid up out of reservoir 26 along a path through fluid connection 40, valve 30, accumulation chamber 29 and connection members 80. This flow of electrolyte creates a washing action behind the measuring aperture 14. If the measuring aperture is open as it will be in operation of the structure 10 the sample 48 will be drawn into the aperture tube 12 at the same time that electrolyte is passing behind aperture 14. The clean electrolyte from reservoir 26 will surround the sample coming through the aperture 14 and prevent particles from straying in the aperture tube 12, thus eliminating the disadvantageous swirling effect of eddy currents as in US. Pat. No. 3,746,976. The washing action created by the flow of electrolyte behind the measuring aperture 14 is such as to ensure that all particles introduced into the aperture tube are caught by the orifice of the second chamber 18 so as to prevent the occurrence of extraneous signals.

The supply reservoir 52 is illustrated in the form of a livestock waterer in order to keep the level 37 of clean electrolyte 28 in reservoir 26 at a constant height. It is necessary to maintain the pressure drop stable so that the flow rate through the aperture 14 will be relatively constant. Since in the arrangement shown it is not possible to measure the volume of sample scanned by the detector. it is mandatory that the flow rates be stable.

It is to be noted that, if desired, the structure of the present invention may be adapted to a closed-loop circulatory system similar to that disclosed in U.S. Pat. No. 3,746,976. This could be accomplished by closing or omitting connection 23, and connecting waste conduit 42 to fluid connection 40 with a pump and filter interposed therebetween. The effective operation of the structure herein would be the same except recirculating electrolyte would flow through structure instead of clean fluid from reservoir 26. 7

FIGS. 2, 3 and 4 illustrate three forms of construction of the aperture tube comprising inner and outer chambers as shown in FIG. 1. In FIG. 2, the orifice 16 is drilled directly into the glass wall of the second chamber 18. A tungsten point is inserted into the wall of the inner chamber 18 before it is sealed into the outer chamber 13. A tiny spot of heat is applied to the intended location of orifice 16 and the dimple 60 is pushed out by the tungsten point when the glass gets hot. The dimple subsequently is ground down flat as shown and the orifice 16 is drilled thereon. The aperture 14 is formed within a wafer which is heat-sealed to the outer chamber 13 in registry with orifice 16 in a known manner.

In the embodiment shown in FIG. 3, a jewel or sapphire wafer having the measuring aperture 14' is mounted on the inside of the tubing which is intended to form the wall of chamber 13'. The hole for the wafer bearing aperture 14' is picked in the opposite side of the tube and the wafer is positioned behind the hole. The wafer and the glass around it are then heated and sealed, such that the wafer is an integral part of the glass tubing. Similarly a wafer with orifice 16' is mounted on the outside of a length of smaller diameter tubing intended to form the inner chamber 18 of the aperture tube.

In the aperture tube shown in FIG. 4, the aperture 14" is formed within a wafer positioned on the wall of the outer chamber 13" in the same manner as that of FIG. 2. The orifice 16" is formed on an upstanding jewel or sapphire 61 which is fused to the wall of chamber 18". The effect and operation of this tube is the same as that of the tube shown in FIG. 2.

After the large bore tubing carrying aperture 14, 14' or 14", and the small bore tubing carrying the respective orifice 16, 16' or 16" are both fabricated, they are held together in a suitable fixture or vise so that the aperture and orifice are in registry with proper spacing between the tubes. The two tubes are then heat-melted and sealed at the locations 50, 50' or 50" to produce the aperture tube as shown. It may be desirable to put a graded seal in both tubes so that the temperature coefficients do not cause breakage of the aperture tube on cooling. This may be avoided if the entire structure is made of glass having the same temperature coefficient as that of the wafer as known in the art.

As indicated previously, the structure of the invention is such that aperture tubes of a construction different from tube 12 may be used by disassembling coupling block 54, removing tube 12 and positioning a new tube. So long as the upper parts of the new tube which are retained in block 54 have the same configuration as tube 12 any of a wide variety of tubes may be used.

In FIG. 5 one such interchangeable alternate form of aperture tube is shown. There is a first tube 113 and a second tube 118. A relatively narrow connecting tube 130 connects the tubes 113 and 118. An aperture 114 is provided in connecting tube 130 and an orifice 116 is provided in the wall of tube 113. Coupling members 125, 162, 121, 170 and 173 corresponding to members 24, 62, 21, 70 and 73 shown in FIG. 1 are provided to enable positioning of the aperture tube assembly on connecting block 54. Oring 164 seals the tube in the block in the same manner as O-ring 64 of FIG. 1. An electrode 134 is located in tube 113 and corresponds to electrode 34.

In operation, after connection in block 54 the circulating flow of clean electrolyte from reservoir 26 comes down through tube 113, passes through orifice 1 16 and connecting tube and then back up through tube 118 into conduit 20 (FIG. 1). Sample simultaneously is sucked into aperture 114 and the circulating flow carries the particles which have been measured from left to right and away from the measuring zone preventing them from returning to the measuring zone. The flow through tubes 113 and 118 is kept at a desired rate by means of the restriction 127 placed upstream of tube 113.

FIGS. 6, 7 and 10 illustrate three further interchangeable alternate forms of aperture tube which may be used in the structure 10. In each figure the upper elements of the tube are shown with conduits and fittings corresponding to like elements of the tube 12 to enable placement of the alternate tube in the connecting block 54. These like elements are identified with the same reference numbers as in FIG. 1 with single, double or triple primes added.

In FIG. 6 the aperture 214 is positioned in the side of a U tube 213 of small diameter measuring about 2.5 mm. A V-shaped restriction 280 is formed in the wall of the U tube opposite the aperture to increase the flow velocity of electrolyte as it passes behind the aperture. The dimensions of the U tube proximate the aperture and V-shaped restriction are on the order of about 1 mm. Clean electrolyte flows down leg 215 and provides a continuous washing effect behind aperture 214 normal to the aperture axis by reason of the restriction 280. The wash electrolyte together with the sample which has been drawn through aperture 214, then leaves the U tube by passing up leg 217 and out into conduit 20. The zone 216 immediately below restriction 280 and behind aperture 214 is roughly equivalent to orifice 16 of aperture tube 12 in that the fluid present in this zone is used wash electrolyte and sample. This fluid immediately is carried away from the mea suring aperture 214 by reason of increased flow rate behind the restriction 280.

In FIGS. 7, 8 and 9, aperture 314 is positioned on tube 313. A V-shaped restriction 380 is formed in the wall of tube 313 opposite the aperture, again for the purpose of increasing the flow velocity of electrolyte as it passes behind the aperture. A capillary tube 317 is positioned within tube 313 and terminates at the lower end 330 of tube 313 below the aperture opening. Clean electrolyte flows down tube 313 to provide the continuous washing effect behind aperture 314 normal to the aperture axis by reason of the restriction 380. The wash electrolyte together with the sample which has been drawn through aperture 314 then leaves the aperture tube by passing up capillary tube 317 and out into conduit 20". The zone 316 immediately below restriction 380 and behind aperture 314 is roughly equivalent to orifice 16 of aperture tube 12 in that the fluid present in this zone is used wash electrolyte and sample. This fluid immediately is carried away from the measuring aperture 314 by reason of increased flow rate behind the restriction 380. The whole assembly is fitted to a coupling block 54 (not shown) as described in connection with FIGS. 1 and 5 for the appropriate liquid and electrical connections.

In the embodiment of FIGS. 10 through 13 aperture 414 is positioned on tube'413 at a location of reduced diameter. A second tube 417 which is open at the bottom 430 of tube 413 is positioned within tube 413 with one wall 420 of tube 417 engaging the back wall 422 of tube 413 along the length thereof. The surface 424 of tube 417 opposite wall 420 is deformed in the shape of a longitudinal channel such that tube 417 is of generally half-moon cross-sectional configuration. A protrusion 480 is formed in surface 424 proximate the back side of aperture 414 to provide the desired increased flow velocity of electrolyte as it passes behind the aperture. The tube 417 terminates below aperture 414 with space below the terminal end for passage of fluid up the tube. The half-moon configuration of tube 417 is such as to divide tube 413 into two portions, a first portion 430 for down-flow of electrolyte and a second portion 432 for up-flow of electrolyte and sample. Proximate the location of aperture 414 the inner tube 417 is completely flat so that wash electrolyte must pass through countersink 440 behind aperture 414, the countersink being formed in the wall of tube 413 when the wafer having aperture 414 is secured to the outside surface of the tube. Another longitudinal depression is formed in tube 417 below the protrusion 480 to permit wash fluid to pass out from behind aperture 414. The radial di mension of the protrusion 480 proximate aperture 414 is as small as possible in order to cause the crosssectional area of the electrolyte between the aperture and electrode to become large as quickly as possible. Clean electrolyte flows down portion 430 of tube 413 to provide the washing effect behind aperture 414 as described. The wash electrolyte and sample which has been drawn through the aperture then passes up tube 417 along portion 432 and out into conduit The restrictions 280, 380 and 480 behind the aperture of the embodiments of FIGS. 6, 7 and 10, respectively, are such as to provide very high electrolyte fiow rates without necessitating the use of large quantities of clean electrolyte. A criterion of performance satisfied by each of the embodiments disclosed herein is that the speed of the washing flow of clean electrolyte down past the measuring aperture is greater than any upward components of any currents formed behind the aperture thus sweeping particles which have already been measured out of the sensing zone and preventing any particles from traveling upwards behind the aperture into the zone immediately upstream thereof where false pulses may be created.

Minor variations in the structure and other variations in the arrangements and size of the various parts may occur to those skilled in the art without departing from the spirit or circumventing the scope of the invention as set forth in the appended claims.

What it is desired to secure by Letters Patent of the United States is:

1. In a particle measuring apparatus including a vessel for containing a body of particulate liquid suspension to be tested, an aperture tube extending into said vessel and including an aperture, fluid moving means for establishing pressure differentials and adapted for moving the suspension from the vessel through the aperture into and through the aperture tube to a waste collection container, a first electrode in the vessel and a second electrode in the aperture tube to establish an electrical field in the aperture between said vessel and the aperture tube, means including elecrical leads connected to the electrodes and adapted to extend connections to a detector to respond to electrical measuring signals produced across said electrodes with passage of particles through said aperture, the aperture tube having an inlet chamber adapted for fluid connection with a source of particle free liquid, said inlet chamber having said aperture in fluid communication on one side thereof with the suspension in the vessel to permit passage of the suspension through the aperture into the inlet chamber, there being a zone in the aperture tube proximate to and downstream of the aperture in which spurious signals may normally be produced, an outlet chamber in fluid connection with said inlet chamber, means for connecting said outlet chamber to said fluid moving means and said Waste collection container, means for initially filling the inlet and outlet chambers with particle free liquid; the improvement comprising, the outlet chamber being formed within the inlet chamber, said chambers having a common closed bottom wall, said aperture tube having a restriction in the path of flow of said particle free liquid to cause the flow ve locity thereof to increase in the spurious signal producing zone and continuously to wash the zone simultaneously with passage of the suspension through the aperture such that particles which have been measured within the aperture and thereafter passing out of the same immediately are swept out of the spurious signal producing zone by the particle free liquid and moved into the outlet chamberv 2. The invention as claimed in claim 1 in which said restriction is an orifice formed in the wall of the outlet chamber in closely-spaced registry with said aperture.

3. The invention as claimed in claim 2 in which the aperture is formed in a wafer which is fused to the wall of the inlet chamber and the orifice is formed on a raised dimple on the wall of the outlet chamber.

4. The invention as claimed in claim 2 in which the aperture and orifice are formed in wafers which are respectively fused to the chamber walls.

5. The invention as claimed in claim 2 in which the aperture is formed in a wafer which is fused to the wall of the inlet chamber and the orifice is formed on an upstanding jewel which is fused to the wall of the outlet chamber.

6. In a particle measuring apparatus including a vessel for containing a body of particulate liquid suspension to be tested, an aperture tube extending into said vessel and including an aperture, fluid moving means for establishing pressure differentials and adapted for moving the suspension from the vessel through the aperture into and through the aperture tube to a waste collection container, a first electrode in the vessel and a second electrode in the aperture tube to establish an electrical field in the aperture between said vessel and the aperture tube, means including electrical leads connected to the electrodes and adapted to extend connections to a detector to respond to electrical measuring signals produced across said electrodes with passage of particles through said aperture, the aperture tube having an inlet chamber adapted for fluid connection with a source of particle free liquid, said inlet chamber having said aperture in fluid communication on one side thereof with the suspension in the vessel to permit passage of the suspension through the aperture into the inlet chamber, there being a zone in the aperture tube proximate to and downstream of the aperture in which spurious signals may normally be produced, an outlet chamber in fluid connection with said inlet chamber, means for connecting said outlet chamber to said fluid moving means and said waste collection container, means for initially filling the inlet and outlet chambers with particle free liquid; the improvement comprising, the inlet chamber including a first tube and a connect ing tube formed normal to the first tube, said outlet chamber being in fluid connection with the connecting tube, said aperture being formed in the connection tube, said aperture tube hairing an orifice formed in the wall of the first tube opening into the connection tube, said orifice being in the path of flow of said particle free liquid to cause the flow velocity thereof to increase in the spurious signal producing zone and continuously to wash and zone simultaneously with passage of the suspension through the aperture such that particles which have been measured within the aperture and thereafter passing out of the same immediately are swept out of the spurious signal producing zone by the particle free liquid and moved into the outlet chamber.

7. In a particle measuring apparatus including a vessel for containing a body of particulate liquid suspension to be tested, an aperture tube extending into said vessel and including an aperture, fluid moving means for establishing pressure differentials and adapted for moving the suspension from the vessel through the aperture into and through the aperture tube to a waste collection container, a first electrode in the vessel and a second electrode in the aperture tube to establish an electrical field in the aperture between said vessel and the aperture tube, means including electrical leads connected to the electrodes and adapted to extend connections to a detector to respond to electrical measuring signals produced across said electrodes with passage of particles through said aperture, the aperture tube having an inlet chamber adapted for fluid connection with a source of particle free liquid, said inlet chamber having said aperture in fluid communication on one side thereof with the suspension in the vessel to permit passage of the suspension through the aperture into the inlet chamber, there being a zone in the aperture tube proximate to and downstream of the aperture in which spurious signals may normally be produced, an outlet chamber in fluid connection with said inlet chamber, means for connecting said outlet chamber to said fluid moving means and said waste collection container, means for initially filling the inlet and outlet chambers with particle free liquid; the improvement comprising, the aperture tube being of generally U-shaped configuration with one leg forming the inlet chamber and the other leg forming the outlet chamber, said aperture tube having a restriction in the path of flow of said particle free liquid to cause the flow velocity thereof to increase in the spurious signal producing zone and continuously to wash the zone simultaneously with passage of the suspension through the aperture such that particles which have been measured within the aperture and thereafter passing out of the same immediately are swept out of the spurious signal producing zone by the particle free liquid and moved into the outlet chamber.

The invention as claimed in claim 7 in which said restriction is a generally V-shaped deformation in the wall of the tube extending therewithin opposite the aperture.

9. In a particle measuring apparatus including a ves sel for containing a body of particulate liquid suspension to be tested, an aperture tube extending into said vessel and including an aperture, fluid moving means for establishing pressure differentials and adapted for moving the suspension from the vessel through the aperture into and through the aperture tube to a waste collection container, a first electrode in the vessel and a second electrode in the aperture tube to establish an electrical field in the aperture between said vessel and the aperture tube, means including electrical leads connected to the electrodes and adapted to extend connections to a detector to respond to electrical measuring signals produced across said electrodes with passage of particles through said aperture, the aperture tube having an inlet chamber adapted for fluid connection with a source of particle free liquid, said inlet chamber having said aperture in fluid communication on one side thereof with the suspension in the vessel to permit passage of the suspension through the aperture into the inlet chamber, there being a zone in the aperture tube proximate to and downstream of the aperture in which spurious signals may normally be produced, an outlet chamber in fluid connection with said inlet chamber, means for connecting said outlet chamber to said fluid moving means and said waste collection container, means for initially filling the inlet and outlet chambers with particle free liquid; the improvement comprising, the outlet chamber being a capillary tube formed within the inlet chamber, the inlet chamber having a closed bottom, the outlet chamber terminating at the closed bottom of the inlet chamber at an open end positioned below the aperture, said aperture tube having a restriction in the path of flow of said particle free liquid to cause the flow velocity thereof to increase in the spurious signal producing zone and continuously to wash the zone simultaneously with passage of the suspension through the aperture such that particles which have been measured within the aperture and thereafter passing out of the same immediately are swept out of the spurious signal producing zone by the particle free liquid and moved into the outlet chamber.

10. The invention as claimed in claim 9 in which said restriction is a generally V-shaped deformation in the wall of the inlet chamber opposite the aperture.

1 1. In a particle measuring apparatus including a vessel for containing a body of particulate liquid suspen sion to be tested, an aperture tube extending into said vessel and including an aperture, fluid moving means for establishing pressure differentials and adapted for moving the suspension from the vessel through the aperture into and through the aperture tube to a waste collection container, a first electrode in the vessel and a second electrode in the aperture tube to establish an electrical field in the aperture between said vessel and the aperture tube, means including electrical leads con nected to the electrodes and adapted to extend connections to a detector to respond to electrical measuring signals produced across said electrodes with passage of particles through said aperture, the aperture tube having an inlet chamber adapted for fluid connection with a source of particle free liquid, said inlet chamber having said aperture in fluid communication on one side thereof with the suspension in the vessel to permit passage of the suspension through the aperture into the inlet chamber, there being a zone in the aperture tube proximate to and downstream of the aperture in which spurious signals may normally be produced, an outlet chamber in fluid connection with said inlet chamber,

means for connecting said outlet chamber to said fluid moving means and said waste collection container, means for initially filling the inlet and outlet chambers with particle free liquid; the improvement comprising, the outlet chamber being formed within the inlet chamber. the inlet chamber having a closed bottom, the outlet chamber terminating at the closed bottom of the inlet chamber at an open end positioned below the aperture, said aperture tube having a restriction in the path of flow of said particle free liquid to cause the flow velocity thereof to increase in the spurious signal producing zone and continuously to wash the zone simultaneously with passage of the suspension through the aperture such that particles which have been measured within the aperture and thereafter passing out of the same immediately are swept out of the spurious signal producing zone by the particle free liquid and moved into the outlet chamber.

12. The invention as claimed in claim 11 in which said restriction is a protrusion in the wall of the outlet chamber opposite the aperture.

13. The invention as claimed in claim 12 in which longitudinal portions of the walls of the chambers are disposed in abutting relationship and the wall of the outlet chamber opposite the abutting wall is deformed in the shape of a longitudinal channel to provide said inlet chamber.

14. An aperture tube for use in particle measuring apparatus including a container of particulate liquid suspension into which the aperture tube extends, said tube comprising, an inlet chamber, an outlet chamber in fluid connection with the inlet chamber, said outlet chamber being formed within the inlet chamber, the chambers having a common closed bottom wall, the inlet chamber having an aperture adapted to be in communication on one side thereof with the liquid suspension, there being a zone in the aperture tube proximate to and downstream of the aperture in which spurious signals may normally be produced, means for connecting the inlet chamber to a source of particle free liquid, means for connecting the outlet chamber to fluid moving means to move the suspension from the container through the aperture into the spurious signal producing zone, the tube having a restriction in the path of flow of the particle free liquid to cause the flow velocity thereof to increase in the spurious signal producing zone and continuously wash the zone simultaneously with passage of the suspension through the aperture such that particles which have passed through the aperture immediately are swept out of the spurious signal producing zone by the particle free liquid and moved into the outlet chamber.

15. The invention as claimed in claim 14 in which said restriction is an orifice formed in the wall of the outlet chamber in closely-spaced registry with said aperture.

16. The invention as claimed in claim 15 in which the aperture is formed in a wafer which is fused to the wall of the inlet chamber and the orifice is formed on a raised dimple on the wall of the outlet chamber.

17. The invention as claimed in claim 15 in which the aperture and orifice are formed in wafers which are respectively fused to the chamber walls.

18. The invention as claimed in claim 15 in which the aperture is formed in a wafer which is fused to the wall of the inlet chamber and the orifice is formed on an upstanding jewel which is fused to the wall of the outlet chamber.

19. An aperture tube for use in particle measuring apparatus including a container or particulate liquid suspension into which the aperture tube extends, said tube comprising, an inlet chamber, an outlet chamber in fluid connection with the inlet chamber, the inlet chamber having an aperture adapted to be in commun cation on one side thereof with the liquid suspension, there being a zone in the aperture tube proximate to and downstream of the aperture in which spurious signals may normally be produced, means for connecting the inlet chamber to a source of particle free liquid, means for connecting the outlet chamber to fluid moving means to move the suspension from the container through the aperture into the spurious signal producing zone, the tube having a restriction in the path of flow of the particle free liquid, the inlet chamber including a first tube and a connecting tube formed normal to the first tube, said outlet chamber being in fluid connection with the connecting tube, said aperture being formed in the connection tube, and said restriction is an orifice formed in the wall of the first tube opening into the connection tube, whereby the flow velocity of the parti cle free liquid increases in the spurious signal producing zone and continuously washes the zone simultaneously with passage of the suspension through the aperture such that particles which have passed through the aperture immediately are swept out of the spurious signal producing zone by the particle free liquid and moved into the outlet chamber.

20. An aperture tube for use in particle measuring apparatus including a container of particulate liquid suspension into which the aperture tube extends, said tube comprising, an inlet chamber, an outlet chamber in fluid connection with the inlet chamber, the tube being of generally U-shaped configuration with one leg forming the inlet chamber and the other leg forming the outlet chamber, the inlet chamber having an aperture adapted to be in communication on one side thereof with the liquid suspension, there being a zone in the aperture tube proximate to and downstream of the aperture in which spurious signals may normally be produced, means for connecting the inlet chamber to a source of particle free liquid, means for connecting the outlet chamber to fluid moving means to move the suspension from the container through the aperture into the spurious signal producing zone, the tube having a restriction in the path of flow of the particle free liquid to cause the flow velocity thereof to increase in the spurious signal producing zone and continuously wash the zone simultaneously with passage of the suspension through the aperture such that particles which have passed through the aperture immediately are swept out of the spurious signal producing zone by the particle free liquid and moved into the outlet chamber.

21. The invention as claimed in claim 29 in which said restriction is a generally V-shaped deformation in the wall of the tube extending therewithin opposite the aperture.

22. An aperture tube for use in particle measuring apparatus including a container of particulate liquid suspension into which the aperture tube extends, said tube comprising, an inlet chamber, a capillary tube outlet chamber formed within the inlet chamber and in fluid connection therewith, the inlet chamber having a closed bottom and an aperture adapted to be in communication on one side thereof with the liquid suspen sion, the outlet chamber terminating at the closed bottom of the inlet chamber at an open end positioned below the aperture, there being a zone in the aperture tube proximate to and downstream of the aperture in which spurious signals may normally be produced, means for connecting the inlet chamber to a source of particle free liquid, means for connecting the outlet chamber to fluid moving means to move the suspension from the container through the aperture into the spurious signal producing zone, the tube having a restriction in the path of flow of the particle free liquid to cause the flow velocity thereof to increase in the spurious signal producing zone and continuously wash the zone simultaneously with passage of the suspension through the aperture such that particles which have passed through the aperture immediately are swept out of the spurious signal producing zone by the particle free liquid and moved into the outlet chamber.

23. The invention as claimed in claim 22 in which said restriction is a generally V-shaped deformation in the wall of the inlet chamber opposite the aperture.

24. An aperture tube for use in particle measuring apparatus including a container of particulate liquid suspension into which the aperture tube extends, said tube comprising, an inlet chamber, an outlet chamber formed within the inlet chamber and in fluid connection therewith, the inlet chamber having a closed bottom and an aperture adapted to be in communication on one side thereof with the liquid suspension, the outlet chamber terminating at the closed bottom of the inlet chamber at an open end positioned below the aperture, there being a zone in the aperture tube proximate to and downstream of the aperture in which spurious signals may normally be produced, means for connecting the inlet chamber to a source of particle free liquid, means for connecting the outlet chamber to fluid moving means to move the suspension from the container through the aperture into the spurious signal producing zone, the tube having a restriction in the path of flow of the particle free liquid to cause the flow velocity thereof to increase in the spurious signal producing zone and continuously wash the zone simultaneously with passage of the suspension through the aperture such that particles which have passed through the aperture immediately are swept out of the spurious signal producing zone by the particle free liquid and moved into the outlet chamber.

25. The invention as claimed in claim 24 in which said restriction is a protrusion in the wall of the outlet chamber opposite the aperture.

26. The invention as claimed in claim 25 in which longitudinal portions of the walls of the chambers are disposed in abutting relationship and the wall of the outlet chamber opposite the abutting wall is deformed in the shape of a longitudinal channel to provide said inlet chamber.

27. An electrolyte supply system for particle measuring apparatus in which an aperture tube is suspended in a vessel for containing a body of particulate liquid suspension to be tested, the tube having an aperture to permit passage of the suspension from the container into the tube, the apparatus including a first electrode in the vessel and a second electrode in the aperture tube to establish an electrical field in the aperture between the vessel and the aperture tube, and means including electrical leads connected to the electrodes and adapted to extend connections to a detector to respond to electrical measuring signals produced across the electrodes with passage of particles through said aperture, said system comprising, the aperture tube having an inlet chamber for introduction of particle free electrolyte, an outlet chamber in fluid connection with the inlet chamber, the aperture tube being mounted at the end opposite the suspended end in a coupling block, an electrolyte reservoir in fluid communication with the inlet chamber, a waste container in fluid communica tion with the outlet chamber, and fluid moving means connected to the waste container, whereby the fluid moving means will cause electrolyte to pass from the reservoir through the inlet and outlet chambers and into the container and simultaneously will draw suspension through the aperture.

28. A system as claimed in claim 27 in which the second electrode is the signal electrode for the particle measuring apparatus, the system including an electrolyte drip chamber and supply conduit interposed be tween the reservoir and inlet chamber, the drip chamber and conduit being shielded with an electrical insulating member.

29. A system as claimed in claim 27 in which the cou' pling block is separable into two portions to permit removal of the aperture tube.

30. A system as claimed in claim 27 in which the outlet chamber is connected to the top of the waste container and the waste container is a waste drip chamber having a drain conduit provided at the bottom thereof terminating below the surface of the waste electrolyte drawn into the waste drip chamber such that the electrical connection between the electrolyte path through the drain conduit and the outlet chamber will be bro ken by reason of droplet formation of the electrolyte as it enters the waste drip chamber.

31. The system as claimed in claim 27 in which the volume of electrolyte in the reservoir is maintained constant by continuous supply from an electrolyte source.

32. The system as claimed in claim 27 in which the fluid moving means comprise a source of vacuum.

' UNITED sTATEs PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. I 3,902, 115 DATED August 26, 1975 INVENTOMS) 1 Walter R. Hogg, 'et al.

H is certified that error appears n the above-identified patent and that said Letters Patent are hereby corrected as shown betow;

Column 9, line 10, read -having for hairing". Column 9, line 15,.read -thefor "and".

Signed and Scaled this A ttesr:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (umnnssimrer of Patents and Trademarks 

1. In a particle measuring apparatus including a vessel for containing a body of particulate liquid suspension to be tested, an aperture tube extending into said vessel and including an aperture, fluid moving means for establishing pressure differentials and adapted for moving the suspension from the vessel through the aperture into and through the aperture tube to a waste collection container, a first electrode in the vessel and a second electrode in the aperture tube to establish an electrical field in the aperture between said vessel and the aperture tube, means including elecrical leads connected to the electrodes and adapted to extend connections to a detector to respond to electrical measuring signals produced across said electrodes with passage of particles through said aperture, the aperture tube having an inlet chamber adapted for fluid connection with a source of particle free liquid, said inlet chamber having said aperture in fluid communication on one side thereof with the suspension in the vessel to permit passage of the suspension through the aperture into the inlet chamber, there being a zone in the aperture tube proximate to and downstream of the aperture in which spurious signals may normally be produced, an outlet chamber in fluid connection with said inlet chamber, means for connecting said outlet chamber to said fluid moving means and said waste collection container, means for initially filling the inlet and outlet chambers with particle free liquid; the improvement comprising, the outlet chamber being formed within the inlet chamber, said chambers having a common closed bottom wall, said aperture tube having a restriction in the path of flow of said particle free liquid to cause the flow velocity thereof to increase in the spurious signal producing zone and continuously to wash the zone simultaneously with passage of the suspension through the aperture such that particles which have been measured within the aperture and thereafter passing out of the same immediately are swept out of the spurious signal producing zone by the particle free liquid and moved into the outlet chamber.
 2. The invention as claimed in claim 1 in which said restriction is an orifice formed in the wall of the outlet chamber in closely-spaced registry with said aperture.
 3. The invention as claimed in claim 2 in which the aperture is formed in a wafer which is fused to the wall of the inlet chamber and the orifice is formed on a raised dimple on the wall of the outlet chamber.
 4. The invention as claimed in claim 2 in which the aperture and orifice are formed in wafers which are respectively fused to the chamber walls.
 5. The invention as claimed in claim 2 in which the aperture is formed in a wafer which is fused to the wall of the inlet chamber and the orifice is formed on an upstanding jewel which is fused to the wall of the outlet chamber.
 6. In a particle measuring apparatus including a vessel for containing a body of particulate liquid suspension to be tested, an apErture tube extending into said vessel and including an aperture, fluid moving means for establishing pressure differentials and adapted for moving the suspension from the vessel through the aperture into and through the aperture tube to a waste collection container, a first electrode in the vessel and a second electrode in the aperture tube to establish an electrical field in the aperture between said vessel and the aperture tube, means including electrical leads connected to the electrodes and adapted to extend connections to a detector to respond to electrical measuring signals produced across said electrodes with passage of particles through said aperture, the aperture tube having an inlet chamber adapted for fluid connection with a source of particle free liquid, said inlet chamber having said aperture in fluid communication on one side thereof with the suspension in the vessel to permit passage of the suspension through the aperture into the inlet chamber, there being a zone in the aperture tube proximate to and downstream of the aperture in which spurious signals may normally be produced, an outlet chamber in fluid connection with said inlet chamber, means for connecting said outlet chamber to said fluid moving means and said waste collection container, means for initially filling the inlet and outlet chambers with particle free liquid; the improvement comprising, the inlet chamber including a first tube and a connecting tube formed normal to the first tube, said outlet chamber being in fluid connection with the connecting tube, said aperture being formed in the connection tube, said aperture tube hairing an orifice formed in the wall of the first tube opening into the connection tube, said orifice being in the path of flow of said particle free liquid to cause the flow velocity thereof to increase in the spurious signal producing zone and continuously to wash and zone simultaneously with passage of the suspension through the aperture such that particles which have been measured within the aperture and thereafter passing out of the same immediately are swept out of the spurious signal producing zone by the particle free liquid and moved into the outlet chamber.
 7. In a particle measuring apparatus including a vessel for containing a body of particulate liquid suspension to be tested, an aperture tube extending into said vessel and including an aperture, fluid moving means for establishing pressure differentials and adapted for moving the suspension from the vessel through the aperture into and through the aperture tube to a waste collection container, a first electrode in the vessel and a second electrode in the aperture tube to establish an electrical field in the aperture between said vessel and the aperture tube, means including electrical leads connected to the electrodes and adapted to extend connections to a detector to respond to electrical measuring signals produced across said electrodes with passage of particles through said aperture, the aperture tube having an inlet chamber adapted for fluid connection with a source of particle free liquid, said inlet chamber having said aperture in fluid communication on one side thereof with the suspension in the vessel to permit passage of the suspension through the aperture into the inlet chamber, there being a zone in the aperture tube proximate to and downstream of the aperture in which spurious signals may normally be produced, an outlet chamber in fluid connection with said inlet chamber, means for connecting said outlet chamber to said fluid moving means and said waste collection container, means for initially filling the inlet and outlet chambers with particle free liquid; the improvement comprising, the aperture tube being of generally U-shaped configuration with one leg forming the inlet chamber and the other leg forming the outlet chamber, said aperture tube having a restriction in the path of flow of said particle free liquid to cause the flow velocity thereof to increase in the spurious signal producing zone aNd continuously to wash the zone simultaneously with passage of the suspension through the aperture such that particles which have been measured within the aperture and thereafter passing out of the same immediately are swept out of the spurious signal producing zone by the particle free liquid and moved into the outlet chamber.
 8. The invention as claimed in claim 7 in which said restriction is a generally V-shaped deformation in the wall of the tube extending therewithin opposite the aperture.
 9. In a particle measuring apparatus including a vessel for containing a body of particulate liquid suspension to be tested, an aperture tube extending into said vessel and including an aperture, fluid moving means for establishing pressure differentials and adapted for moving the suspension from the vessel through the aperture into and through the aperture tube to a waste collection container, a first electrode in the vessel and a second electrode in the aperture tube to establish an electrical field in the aperture between said vessel and the aperture tube, means including electrical leads connected to the electrodes and adapted to extend connections to a detector to respond to electrical measuring signals produced across said electrodes with passage of particles through said aperture, the aperture tube having an inlet chamber adapted for fluid connection with a source of particle free liquid, said inlet chamber having said aperture in fluid communication on one side thereof with the suspension in the vessel to permit passage of the suspension through the aperture into the inlet chamber, there being a zone in the aperture tube proximate to and downstream of the aperture in which spurious signals may normally be produced, an outlet chamber in fluid connection with said inlet chamber, means for connecting said outlet chamber to said fluid moving means and said waste collection container, means for initially filling the inlet and outlet chambers with particle free liquid; the improvement comprising, the outlet chamber being a capillary tube formed within the inlet chamber, the inlet chamber having a closed bottom, the outlet chamber terminating at the closed bottom of the inlet chamber at an open end positioned below the aperture, said aperture tube having a restriction in the path of flow of said particle free liquid to cause the flow velocity thereof to increase in the spurious signal producing zone and continuously to wash the zone simultaneously with passage of the suspension through the aperture such that particles which have been measured within the aperture and thereafter passing out of the same immediately are swept out of the spurious signal producing zone by the particle free liquid and moved into the outlet chamber.
 10. The invention as claimed in claim 9 in which said restriction is a generally V-shaped deformation in the wall of the inlet chamber opposite the aperture.
 11. In a particle measuring apparatus including a vessel for containing a body of particulate liquid suspension to be tested, an aperture tube extending into said vessel and including an aperture, fluid moving means for establishing pressure differentials and adapted for moving the suspension from the vessel through the aperture into and through the aperture tube to a waste collection container, a first electrode in the vessel and a second electrode in the aperture tube to establish an electrical field in the aperture between said vessel and the aperture tube, means including electrical leads connected to the electrodes and adapted to extend connections to a detector to respond to electrical measuring signals produced across said electrodes with passage of particles through said aperture, the aperture tube having an inlet chamber adapted for fluid connection with a source of particle free liquid, said inlet chamber having said aperture in fluid communication on one side thereof with the suspension in the vessel to permit passage of the suspension through the aperture into the inlet chambEr, there being a zone in the aperture tube proximate to and downstream of the aperture in which spurious signals may normally be produced, an outlet chamber in fluid connection with said inlet chamber, means for connecting said outlet chamber to said fluid moving means and said waste collection container, means for initially filling the inlet and outlet chambers with particle free liquid; the improvement comprising, the outlet chamber being formed within the inlet chamber, the inlet chamber having a closed bottom, the outlet chamber terminating at the closed bottom of the inlet chamber at an open end positioned below the aperture, said aperture tube having a restriction in the path of flow of said particle free liquid to cause the flow velocity thereof to increase in the spurious signal producing zone and continuously to wash the zone simultaneously with passage of the suspension through the aperture such that particles which have been measured within the aperture and thereafter passing out of the same immediately are swept out of the spurious signal producing zone by the particle free liquid and moved into the outlet chamber.
 12. The invention as claimed in claim 11 in which said restriction is a protrusion in the wall of the outlet chamber opposite the aperture.
 13. The invention as claimed in claim 12 in which longitudinal portions of the walls of the chambers are disposed in abutting relationship and the wall of the outlet chamber opposite the abutting wall is deformed in the shape of a longitudinal channel to provide said inlet chamber.
 14. An aperture tube for use in particle measuring apparatus including a container of particulate liquid suspension into which the aperture tube extends, said tube comprising, an inlet chamber, an outlet chamber in fluid connection with the inlet chamber, said outlet chamber being formed within the inlet chamber, the chambers having a common closed bottom wall, the inlet chamber having an aperture adapted to be in communication on one side thereof with the liquid suspension, there being a zone in the aperture tube proximate to and downstream of the aperture in which spurious signals may normally be produced, means for connecting the inlet chamber to a source of particle free liquid, means for connecting the outlet chamber to fluid moving means to move the suspension from the container through the aperture into the spurious signal producing zone, the tube having a restriction in the path of flow of the particle free liquid to cause the flow velocity thereof to increase in the spurious signal producing zone and continuously wash the zone simultaneously with passage of the suspension through the aperture such that particles which have passed through the aperture immediately are swept out of the spurious signal producing zone by the particle free liquid and moved into the outlet chamber.
 15. The invention as claimed in claim 14 in which said restriction is an orifice formed in the wall of the outlet chamber in closely-spaced registry with said aperture.
 16. The invention as claimed in claim 15 in which the aperture is formed in a wafer which is fused to the wall of the inlet chamber and the orifice is formed on a raised dimple on the wall of the outlet chamber.
 17. The invention as claimed in claim 15 in which the aperture and orifice are formed in wafers which are respectively fused to the chamber walls.
 18. The invention as claimed in claim 15 in which the aperture is formed in a wafer which is fused to the wall of the inlet chamber and the orifice is formed on an upstanding jewel which is fused to the wall of the outlet chamber.
 19. An aperture tube for use in particle measuring apparatus including a container or particulate liquid suspension into which the aperture tube extends, said tube comprising, an inlet chamber, an outlet chamber in fluid connection with the inlet chamber, the inlet chamber having an aperture adapted to be in communcation on one side thereof with the liquid suspension, there bEing a zone in the aperture tube proximate to and downstream of the aperture in which spurious signals may normally be produced, means for connecting the inlet chamber to a source of particle free liquid, means for connecting the outlet chamber to fluid moving means to move the suspension from the container through the aperture into the spurious signal producing zone, the tube having a restriction in the path of flow of the particle free liquid, the inlet chamber including a first tube and a connecting tube formed normal to the first tube, said outlet chamber being in fluid connection with the connecting tube, said aperture being formed in the connection tube, and said restriction is an orifice formed in the wall of the first tube opening into the connection tube, whereby the flow velocity of the particle free liquid increases in the spurious signal producing zone and continuously washes the zone simultaneously with passage of the suspension through the aperture such that particles which have passed through the aperture immediately are swept out of the spurious signal producing zone by the particle free liquid and moved into the outlet chamber.
 20. An aperture tube for use in particle measuring apparatus including a container of particulate liquid suspension into which the aperture tube extends, said tube comprising, an inlet chamber, an outlet chamber in fluid connection with the inlet chamber, the tube being of generally U-shaped configuration with one leg forming the inlet chamber and the other leg forming the outlet chamber, the inlet chamber having an aperture adapted to be in communication on one side thereof with the liquid suspension, there being a zone in the aperture tube proximate to and downstream of the aperture in which spurious signals may normally be produced, means for connecting the inlet chamber to a source of particle free liquid, means for connecting the outlet chamber to fluid moving means to move the suspension from the container through the aperture into the spurious signal producing zone, the tube having a restriction in the path of flow of the particle free liquid to cause the flow velocity thereof to increase in the spurious signal producing zone and continuously wash the zone simultaneously with passage of the suspension through the aperture such that particles which have passed through the aperture immediately are swept out of the spurious signal producing zone by the particle free liquid and moved into the outlet chamber.
 21. The invention as claimed in claim 19 in which said restriction is a generally V-shaped deformation in the wall of the tube extending therewithin opposite the aperture.
 22. An aperture tube for use in particle measuring apparatus including a container of particulate liquid suspension into which the aperture tube extends, said tube comprising, an inlet chamber, a capillary tube outlet chamber formed within the inlet chamber and in fluid connection therewith, the inlet chamber having a closed bottom and an aperture adapted to be in communication on one side thereof with the liquid suspension, the outlet chamber terminating at the closed bottom of the inlet chamber at an open end positioned below the aperture, there being a zone in the aperture tube proximate to and downstream of the aperture in which spurious signals may normally be produced, means for connecting the inlet chamber to a source of particle free liquid, means for connecting the outlet chamber to fluid moving means to move the suspension from the container through the aperture into the spurious signal producing zone, the tube having a restriction in the path of flow of the particle free liquid to cause the flow velocity thereof to increase in the spurious signal producing zone and continuously wash the zone simultaneously with passage of the suspension through the aperture such that particles which have passed through the aperture immediately are swept out of the spurious signal producing zone by the particle free liquid and moved into the outlet chamBer.
 23. The invention as claimed in claim 22 in which said restriction is a generally V-shaped deformation in the wall of the inlet chamber opposite the aperture.
 24. An aperture tube for use in particle measuring apparatus including a container of particulate liquid suspension into which the aperture tube extends, said tube comprising, an inlet chamber, an outlet chamber formed within the inlet chamber and in fluid connection therewith, the inlet chamber having a closed bottom and an aperture adapted to be in communication on one side thereof with the liquid suspension, the outlet chamber terminating at the closed bottom of the inlet chamber at an open end positioned below the aperture, there being a zone in the aperture tube proximate to and downstream of the aperture in which spurious signals may normally be produced, means for connecting the inlet chamber to a source of particle free liquid, means for connecting the outlet chamber to fluid moving means to move the suspension from the container through the aperture into the spurious signal producing zone, the tube having a restriction in the path of flow of the particle free liquid to cause the flow velocity thereof to increase in the spurious signal producing zone and continuously wash the zone simultaneously with passage of the suspension through the aperture such that particles which have passed through the aperture immediately are swept out of the spurious signal producing zone by the particle free liquid and moved into the outlet chamber.
 25. The invention as claimed in claim 24 in which said restriction is a protrusion in the wall of the outlet chamber opposite the aperture.
 26. The invention as claimed in claim 25 in which longitudinal portions of the walls of the chambers are disposed in abutting relationship and the wall of the outlet chamber opposite the abutting wall is deformed in the shape of a longitudinal channel to provide said inlet chamber.
 27. An electrolyte supply system for particle measuring apparatus in which an aperture tube is suspended in a vessel for containing a body of particulate liquid suspension to be tested, the tube having an aperture to permit passage of the suspension from the container into the tube, the apparatus including a first electrode in the vessel and a second electrode in the aperture tube to establish an electrical field in the aperture between the vessel and the aperture tube, and means including electrical leads connected to the electrodes and adapted to extend connections to a detector to respond to electrical measuring signals produced across the electrodes with passage of particles through said aperture, said system comprising, the aperture tube having an inlet chamber for introduction of particle free electrolyte, an outlet chamber in fluid connection with the inlet chamber, the aperture tube being mounted at the end opposite the suspended end in a coupling block, an electrolyte reservoir in fluid communication with the inlet chamber, a waste container in fluid communication with the outlet chamber, and fluid moving means connected to the waste container, whereby the fluid moving means will cause electrolyte to pass from the reservoir through the inlet and outlet chambers and into the container and simultaneously will draw suspension through the aperture.
 28. A system as claimed in claim 27 in which the second electrode is the signal electrode for the particle measuring apparatus, the system including an electrolyte drip chamber and supply conduit interposed between the reservoir and inlet chamber, the drip chamber and conduit being shielded with an electrical insulating member.
 29. A system as claimed in claim 27 in which the coupling block is separable into two portions to permit removal of the aperture tube.
 30. A system as claimed in claim 27 in which the outlet chamber is connected to the top of the waste container and the waste container is a waste drip chamber having a drain conduit provided at the bottom thereof terminating beloW the surface of the waste electrolyte drawn into the waste drip chamber such that the electrical connection between the electrolyte path through the drain conduit and the outlet chamber will be broken by reason of droplet formation of the electrolyte as it enters the waste drip chamber.
 31. The system as claimed in claim 27 in which the volume of electrolyte in the reservoir is maintained constant by continuous supply from an electrolyte source.
 32. The system as claimed in claim 27 in which the fluid moving means comprise a source of vacuum. 